Amino acid transfer RNA has been implicated to play additional regulatory roles in cellular metabolism besides classical protein synthesis. By using Xenopus laevis embryos as a model developmental system we hope to help answer the questions concerning the role of tRNA in cellular control and differentiation. Our research will consist of an extensive study of the tRNAs in Xenopus laevis, their changes as a function of development, and alterations of tRNAs as effected by thyroid hormone in constitutive and regenerative tissues.